Retrograde amnesia and hippocampal stimulation: Dependence upon the nature of associations formed during conditioning

Abstract

The present series of experiments was designed (1) to determine the nature of the associative learning processes which occur during conditioning in a one-trial step-through passive avoidance paradigm commonly used to assess the effects of a variety of agents on memory processes and (2) to determine whether or not postconditioning electrical stimulation of the dorsal hippocampal formation, at current levels subthreshold for the production of afterdischarge activity, produces memory deficits as a function of the nature of the associative learning processes which occur during conditioning. Using noncontingent and response-contingent footshock conditioning procedures, a behavioral analysis demonstrated that both classical fear conditioning and instrumental punishment conditioning contribute to retention test response suppression in rats trained in the step-through passive avoidance paradigm. Postconditioning hippocampal stimulation produces retention deficits in animals trained in the response-contingent conditioning procedure but not in animals trained in the noncontingent conditioning procedure. The data suggest that the effects of postconditioning hippocampal stimulation on retention depend upon the nature of the associative learning processes which occur during conditioning and which are dictated by the procedural details of the conditioning paradigm.